Optical switches are devices for directing optical signals along selected fibers of an optical network, in which light signals are transmitted along optical fibers to transfer information from one location to another. Desirable optical switch characteristics include: high speed switching, low optical insertion loss, long operation lifetime, small size, and low cost. Optical switches are key components in present-day optical networks, analogous to electrical switches in electrical networks. However, optical switches have not been widely adopted due to lack of reliability and to high cost associated with fabrication difficulty.
In an optical switch, light must be accurately coupled to an optical fiber to reduce loss. The alignment requirements of modern single mode optical fibers are particularly stringent, since their core diameters are typically as small as 2 to 10 microns and their acceptance angle is fairly narrow. Insertion loss due to switch-fiber misalignment reduces the amplitude of the optical signal. Therefore, optical switches which accept light from an input optical fiber, and which selectively couple that light to any of a plurality of output optical fibers, must transfer that light with precise alignment and within the small acceptance angle for light to efficiently couple to the fiber. Most prior art optical switches are based on mechanical movement to switch light beams, and consequently have drawbacks including slow switching time and reduced reliability. To avoid these drawbacks, it is desirable for optical switches to direct light beams without moving parts. Such lack of moving parts is a feature generally associated with high reliability and high speed.
Many types of non-mechanical optical switches have been developed for commercial applications, such as switches based on thermal heating, electro-optic phase retardation, and magneto-optic polarization rotation. These devices use various materials and configurations. Thermal heating based switches typically rely on thin film waveguide construction having a long interaction length (e.g., U.S. Pat. No. 5,892,863). This type of switch has a disadvantage of large insertion loss due to fiber to thin film waveguide coupling loss. On the other hand, a micro-optic assembly generally provides low optical loss. Liquid crystal materials have been demonstrated for optical path switching in a micro-optic platform. This type of organic device, however, has disadvantages including slow operation at low temperature and a requirement for a transparent electrode in the optical path (e.g., U.S. Pat. No. 4,917,452).
Oxide materials such as magneto-optic and electro-optic materials are particularly attractive for micro-optic devices. Inorganic materials are generally preferred over organic materials in optical network devices, due to their excellent stability. Optical switches based on magneto-optic crystals have been described in several patents (e.g., in U.S. Pat. Nos. 5,724,165, 5,867,291, 5,912,748, 6,097,518, 6,134,358, 6,137,606, 6,166,838, 6,192,174, 6,212,313, and 6,275,312). However, these optical switches are typically limited to a small number of ports (e.g., 1×2 and 2×2 configurations). Furthermore, even for a small number of optical ports, these configurations tend to be costly to manufacture due to tight fiber alignment tolerance requirements and complex configurations that require many optical elements.
Accordingly, it would be an advance in the art to provide a simple non-mechanical optical switch that is readily scalable to switches having more than 2 output (or input) ports and is suitable for volume production. It is particularly desirable to provide optical switches having a large number of ports, low optical insertion loss, and high speed switching that are also reliable and require only a small number of components which can be miniaturized and are easy to manufacture.